How to reduce the probability of thyristor burning

Aug 18, 2022


Thyristor is the heart of medium frequency power supply of medium frequency furnace

Thyristor is the heart of medium frequency power supply of medium frequency furnace. Its correct use is crucial to the operation of the equipment. It is normal to occasionally damage several thyristors during the use of the intermediate frequency furnace. If the silicon is often burned, it will cause alarm. The working current of thyristor is several thousand amperes, and the voltage is usually one or two thousand volts. Good main control board protection and good water-cooling conditions are necessary.

Overload characteristic of thyristor: damage of thyristor is called breakdown. Under normal water cooling conditions, the current overload capacity can reach more than 110%; No voltage overload capacity, that is to say, silicon is definitely damaged under overpressure. Considering the surge voltage, manufacturers often select silicon components according to 3-4 times of the working voltage when manufacturing equipment. For example, when the rated working voltage of the intermediate frequency cabinet is 1750V, select two silicon elements with a withstand voltage of 2500V to work in series, which is equivalent to a withstand voltage of 5000v.

Correct installation pressure of thyristor: 150-200kg / cm2. When the equipment leaves the factory, it is generally pressed with an oil press. This value can not be reached manually with the maximum force of an ordinary wrench, so there is no need to worry about silicon being crushed during manual pressing; If it is pressed loosely, it will burn silicon due to poor heat dissipation.

Silicon controlled radiator structure: water-cooled cavity + multi copper column support. If the circulating water is too hard, it will scale inside the water chamber, resulting in poor heat dissipation; If leaves and other sundries enter the water chamber, the water flow will be blocked.

The factory test temperature of the thyristor is 100 ℃ (junction temperature). Generally, the normal operation of the electric cabinet can be ensured if the circulating water temperature of the electric cabinet is kept below 45 ℃. The hand-held infrared thermometer is very useful. The 350 ℃ thermometer is only a few hundred yuan, not too expensive. It can be used to measure the temperature of the thyristor and the radiator of the working power supply, so as to find the abnormal point and handle the fault in time.

The table top of the radiator must match the size of the element table top to prevent the device from being damaged due to bias and skew. The radiator table must have high flatness and smoothness. It is recommended that the surface roughness of radiator is less than or equal to 1.6 μ m. Flatness less than or equal to 30 μ m。 During installation, the element table and radiator table shall be kept clean and free of dirt such as oil stain.

During installation, keep the silicon element table and the radiator table completely parallel and concentric. During installation, it is required to apply pressure through the center line of the element so that the pressure is evenly distributed throughout the contact area. When the user manually installs, it is recommended to use a torque wrench to alternately and evenly apply force to all fastening nuts, and the pressure shall meet the specified requirements.

When reusing the water-cooled radiator, special attention shall be paid to check whether the table top is clean and flat, whether there is scale and blockage in the water chamber, and whether the table top is sunken. If the above situation occurs, it shall be replaced.